In recent years, following the spread of utilization of the Internet, a large-scale information search system has been constructed by mutually connecting various databases, with the result that the number of databases users can access has been rapidly increased. On the other hand, with the reduction in size of computer apparatuses and the progress of the mobile communication technology, the mobile computing technology has also been largely developed wherein accesses are made from visiting remote places via radio communication channels and the like. In the development of the technology, the construction of an advanced search system has been strongly desired that can quickly acquire information users aim at, using a simple technique.
Presently, for the search using the Web on the Internet, there are available a search method wherein a plurality of words are inputted and relationships between them are defined using only the AND, OR and NOT logical operators, and a full text search method wherein a natural language is inputted and a morphemic analysis is conducted to extract words, thereby implementing a search. According to this full text search method, it is possible to prompt a user to input a keyword composed of a natural language or words and, based on the inputted keyword, retrieve information matching such a keyword. There is also a directory search method wherein a category a user takes an interest in is traced by tracing an intended item among preclassified categories, thereby retrieving data that can be speculated from such an interest.
On the other hand, as a conventional search technique, there is one that, by using a cluster representative structure as an index relative to document clusters having been subjected to clustering in advance, enables an analogous document search taking a sentence structure into account even when a large-scale document set is a search object (e.g. see JP-A-2001-84252, pp. 4-5, FIG. 1). There is also a technique wherein case data obtained by extracting respective case sentences from electronic documents described in natural language and classifying them is stored in a case database and comparison is made between an inputted search sentence and the case sentences classified and stored in the case database (e.g. JP-A-2000-276487, pp. 8-9, FIG. 1). Further, there is also a technique wherein an inference using domain-dependent conceptual knowledge is made so as to obtain a search result with small search garbage through semantic structural comparison (e.g. see JP-A-2000-242650, pp. 4-5, FIG. 2).
There is also a technique wherein concepts of information managed in databases are registered in an ontology with an array that depends on abstraction degrees of the respective concepts, thereby to produce a database selection menu based on the concepts registered in the ontology and perform maintenance and management of the database selection menu (e.g., see JP-A-2000-222436, pp. 5, FIG. 1). Further, there is also a technique wherein a plurality of search conditions and dates are inputted and search conditions are combined using ontologies with respect to the individual conditions (e.g. see JP-A-H11-126209, pp. 8, FIG. 5).
Thus, it is seen that a full text search engine being the foregoing existent search user interface, although it is easy for a user to input, but difficult to perform an accurate search. On the other hand, in case of a directory search engine, it is easy to search for intended information because it can be speculated from a user's interest, but, inasmuch as directories are formed with a predetermined structure, expansion is difficult, thus lacking in flexibility.
Further, according to the techniques described in the above cited literature it is set as an ideal to input a natural language as a search key, so that there is limitation in terms of accurately inputting a user's high-level search request. Further, according to the technique described in JP-A-2000-222436 (pp. 5, FIG. 1), it is necessary to manually carry out maintenance and management of database search menus, so that loads thereof become extremely large at the present time when addition and deletion of various databases are frequently implemented. Furthermore, according to the technique described in JP-A-H11-126209 (pp. 8, FIG. 5), inasmuch as ontologies are strictly applied to the search conditions, it can not deal with a user's high-level search request.
Recently, a new Web scheme called “Semantic Web” has been proposed as the concept of next generation Web by the W3C (World Wide Web Consortium) being the international standardization organization about Web. A working group has started in the W3C in February 2001 and submitted DAML+OIL (DARPA Agent Markup Language/Ontology Inference Language) as an ontology language at the end of 2001. Following it, also in Japan, AIDOS (Advanced Integrated Documents Standardization committee) of Information Technology Research and Standardization Center of Japanese Standards Association, Semantic Web Committee of Interoperability Technology Association for Information Processing, Japan, have been actively operating for standardization.
This “Semantic Web” gives semantics (semantic information) on Web sites as metadata and creates spaces where data can be mechanically processed without using human hands. Based on XML and formalizing semantic information of a data structure, an agent can automatically understand the meaning and perform processing. For example, in the current search system, if a search is conducted using both “Yokohama” and “travel agent”, a travel agent of Tokyo planning a Yokohama Harbor tour is also retrieved, so that it is necessary for a user to exclude unnecessary information based on the search result. In case of “Semantic Web”, if a place of an agent is given as metadata on a Web page, “travel agents located in Yokohama” is mechanically retrieved.
Presently, it is very difficult to conduct a search corresponding to a high-level need. When the foregoing “Semantic Web” is generally constructed, such a search that is more accurate than the keyword-based full text search widely used at present is desirable. Specifically, for enabling a further intellectual search on “Semantic Web” being the next generation Web, an advanced user interface that can describe relationships between metadata is desirable.